Chemical mechanical polishing is becoming a common process for forming interconnects within a semiconductor device. Currently, in-laid interconnects, whether single or dual, are being developed for use in advanced semiconductor devices. Typically, the interconnects include copper or aluminum. During the polishing process, a slurry that includes a liquid and particles, such as alumina particles, is used to remove portions of the conductive layer that overlie an insulating layer. After the removal step, the substrate surface is cleaned. During this cleaning step, the surface of the insulating layer, which is typically oxide, has a negative charge and attracts positively charged particles. Alumina has an isoelectric point at a pH of approximately 9. Therefore, in the presence of water, which has a pH of approximately 7, the oxide surface will have a negative charge and will attract the positively charged alumina particles.
One way to remove the particles is to increase the pH of the solution by adding ammonium hydroxide so that the positively charged alumina particles become negatively charged and are repelled by the oxide surface. While this works for tungsten, it is difficult to use a solution with a high pH for aluminum or copper because ammonia will react with copper to form copper-ammonium complexes, or, in the case of aluminum, will attack the aluminum causing corrosion or pits.